Sputtering ion source for producing an ion beam comprising ions of a solid material



July 16, 1968 H ET AL 3,393,339

SPUTTERING ION SUURCE FOR PRODUCING AN ION BEAM COMPRISING IONS OF ASOLID MATERIAL Filed July 8, 1965 United States Patent Ofice 3,393,339Patented July 16, 1968 3,393,339 SPUTIERING ION SOURCE FOR PRODUCING ANION BEAM COMPRISING IONS OF A' SOLID MATERIAL Kenneth Jefiery Hill,Didcot, and Richard Stuart Nelson,

Goring-on-Thames, England, assignors to United Kingdom Atomic EnergyAuthority, London, England Filed July 8, 1965, Ser. No. 470,441 Claimspriority, application Great Britain, July 13, 1964, 28,900/ 64 7 Claims.(Cl. 313-230) ABSTRACT OF THE DISCLOSURE A sputtering ion source forproducing an ion beam comprising ions of a solid material has .ahelically coiled D.C. energized filament mounted in a low pressuregaseous atmosphere adjacent to and coaxial with an end surface of afirst electrode formed of said material whereby electrons from thefilament ionize the gas and the gas ions strike the electrode releasingatoms therefrom. These atoms are in turn ionized and the magnetic fieldof the filament tends to concentrate them on the axis. A furtherapertured electrode is provided to extract the ions thus concentrated onthe axis and project them as a beam in a direction away from the firstelectrode.

This invention relates to ion sources.

Known ion sources commonly produce ions of inert gases. For somepurposes, however, a beam comprising ions of a solid material isrequired, for example in investigating the damage resulting from thebombardment of a solid body with ions of the same or a different solid.Ion sources have been made for producing beams comprising ions of ametal, but these sources have had several disadvantages. Thus it isnecessary for the metal to be vaporised initially, and this necessitatesa very high temperature. To reduce the temperature which has to beattained a salt of the metal, frequently the metal chloride, has beenused instead, but this has the further disadvantage of introducingchlorine ions into the beam produced. Also, in the case of some metals,for example gold, the chloride dissociates before it vaporises.

An object of the present invention is to provide a sputtering ion sourcein which these disadvantages are largely overcome.

According to the present invention, a sputtering ion source forproducing an ion beam comprising ions of a solid material, includes asputtering electrode having a surface formed of said material, means toenergise the sputtering electrode, a coiled filament mounted adjacentsaid surface, means at least initially to supply a gas at low pressureto the region of the filament such that it emits electrons which ioniseatoms of said gas and of said material produced by the collision of ionswith said surface, the energised filament having an associated magneticfield which tends to concentrate the emitted electrons in the region ofthe axis of the filament, and an accelerating electrode positioned onthe side of the filament away from said surface which electrode drawions from the region of the filament to form said ion beam.

A sputtering ion source in accordance with the present invention willnow be described by way of example with reference to the accompanyingdrawing, which shows a central cross section through the source.

The source will initially be described as producing a beam of copperions. Referring now to the drawing, the source comprises a sputteringelectrode 1 formed of copper and screwed on to a copper mounting 2 whichpasses out of the rear of the source through an insulator 3. The forwardend of the sputtering electrode 1 has a surface 4 which is closelyadjacent a coiled tungsten filament 5. The sputtering electrode 1 andthe filament 5 are contained within a stainless steel housing 6 into therear of Which an inert gas such as xenon is passed by way of a bore 7through the insulator 3. Xenon is generally preferred to say argon asthe heavier gas has a better sputtering ratio. At the forward end of thehousing 6 is an ion exit aperture 8 formed in a graphite member 9, and agraphite accele rating electrode 10 having an aperture 11 aligned withthe aperture 8.

Although not shown in the drawing, provision is made for cooling thesource with air during use.

During operation the accelerating electrode 10 is maintained at earthpotential, thehousing 6 and hence also the member 9 at 1 to 20 kilovoltspositive with respect to earth, the filament 5 at 0 to 200 voltsnegative with respect to the housing 6, and the sputtering electrode 1at 2,000 volts negative with respect to the housing 6. The voltageacross the filament 5 is about 3 volts and the current about 40 amps.

The operatiOn is then as follows. Electrons driven off the filament 5ionise atoms of xenon, some of the resulting xenon ions striking thesurface 4 of the sputtering elec trode 1 releasing atoms of copper.These copper atoms are also ionised by electrons from the filament 5.This ionisation occurs in the region of the filament 5 because themagnetic field associated with the filament 5 tends to concentrate theemitted electrons near the axis of the filament 5. The region of thefilament 5 therefore contains a plasma which includes ions of copper andxenon. The accelerating electrode 10 draws these ions from the plasma sothat a beam of these ions emerges from the aperture 11.

To obtain satisfactory operation the pressure of xenon need only beabout l0 mm. mercury initially, and in a particular embodiment of thesource described the percentage of copper ions in the beam may forexample be about 50% and the beam about 1 milliamp. This percentagetends to increase with the time since switching the source on. It canalso be increased by decreasing the supply of xenon whilst adjusting thevoltages to maintain the arc. In this way a self-supporting copper arecan be achieved and the resulting beam approaches copper ions.

As the source can be made entirely of metal and glass, .and as theapertures 8 and 11 are only about 1 mm. and 1.5 mm. respective-1y indiameter, the source is very suitable for use in association with lowpressure equipment.

To produce a beam of ions other than copper, a sputtering electrode ofthe desired material is substituted. It will be appreciated that theoperation is such that an ion beam can be obtained even from a materialsuch as tungsten having a very high melting point. Where the material tobe used is expensive, for example if gold is to be used, the mounting 2can be extended so that the sputtering electrode 1 can be much shorter.

In addition to uses in the study of radiation damage, the source may,for example, be used in mass spectroscopy or mass separators.Furthermore, because a beam comprising a very high percentage of metal,say copper, ions can be achieved, the source can be used to produceelectric conductors for printed electric circuits or microcircuits. Thebeam may either be sufficiently focussed to enable the desired patternof conductors to be written, or a more diffuse beam may be used and thedesired pattern obtained 'by masking.

We claim:

1. A sputtering ion source for producing an ion beam comprising ions ofa solid material including a sputtering electrode having an end surfaceformed of said material, a filament formed by a helical coil mountedadjacent to said end surface with the axis of the coil intersecting saidp i a 3 v end surface, duct means for gas at wr'r issvr o t e si 9f themen sa qrfi a-s nientningaanstiaeted such that when energized by adirect current it emits electrons which ionize atoms of said gas, andions of said material are produced by the collision of said gas i onswith said surface, the shape of said helical coil filament being suchthat the magnetic field created lupon energization of the filament tendsto concentratef the emitted electrons in the region of said axis, andincluding; an accelerating electrode means positioned along the saidaxis on the side of filament away from the said surface for drawing ionsfrom the said region to form 'sai'dfionbeam." 2. A sputtering ion sourceas claimed in claim 1 wherein said sputtering electrode is cylindricaland has an end of circular cross-section forming said end surface, theaxis of said end surface being coincident'with said coil axis.

3. A sputtering ion source as claimed in claim 2 including means forvarying the pressure of the gas entering the ion source for varying thepercentage of ions of said material in the said ion beam.

4. A sputtering ion source as claimed in claim 3 wherein the saidmaterial is copper and the said gas is Xenon.

5. A sputtering ion source for producing an ion beam comprising ions ofa solid material, including a sputtering electrode of cylindricalcross-section having an end surface formed of said material, a filamentformed by a helical coil mounted adjacent to and coaxial with said endat least initially supplying a a surface, a duct through l A l ,t Vwhich,'at least initially, g'a's'is sup d at 210W nre s etqt eregion of.the. filament, means for energizing the filament with direct currentsuch that it emits electrons which ionize atoms of said gas and of saidmaterial produced by the collision of ions with said surface, themagnetic field associated with the energized filament being such as totend to concentrate the emitted electrons in'the region of the axis ofthe filament, and an accelerating electrode positioned on th'e'side' ofthe filament away from said end surface, which-electrode draws ions fromtheLregi n'of the filament to form said ionbeam. r I

6. A sputtering ion source as claimed in'claim 5 wherein the pressure ofthe gas is regulated to vary the percentage of ions of said materialin-the ion beam.

7. A sputtering ion source as claimed in claim 6 wherein the saidmaterial is copper'and the said gas is xenon.

References Cited UNITED STATES PATENTS 2,772,363 11/1956 Robinson '25041.9' 2,947,868 8/1960 Herzog 250-419 JAMES W. LAWRENCE, Prin'z'aiy Exammar: ROBERT JUDD, Assistant Examiner.

